Route guidance systems, methods, and programs

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2005-346663 filed on Nov. 30, 2005, including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Related Technical Fields

Related technical fields include route guidance systems, methods, and programs.

2. Description of the Related Art

A navigation apparatus mounted on a vehicle detects a current position of the vehicle by GPS (global positioning system), reads out map data from a data storing section, displays a map screen on a display section, and displays the vehicle position on a map of the area surrounding the vehicle. Therefore, a driver of the vehicle may drive the vehicle using the vehicle position displayed on the map as an aid.

When the driver inputs a destination and sets a route search condition, a route from the current position as a starting point to the destination is searched on the basis of the search condition. The searched route is displayed together with the vehicle position on the map, and the driver is provided guidance along the searched route. Therefore, the driver may drive the vehicle following the searched route.

During route guidance, when there is a specific intersection at which the vehicle must turn right or left, additional guidance is executed, such as by voice output, for example, before the vehicle arrives at the intersection. In order for route guidance to be executed, one or more guidance points are set at locations at set distances before the turn intersection along the specified route. When the vehicle arrives at the guidance points, additional guidance for each of the guidance points is output by voice. Such a system is described in Japanese Patent Application Publication No. JP-A-6-295399.

Also, if the road traveled to the guidance intersection has a plurality of roads, a specific lane is set as a recommended lane, and lane guidance is provided so that the vehicle will drive in the recommended lane.

SUMMARY

However, in the conventional navigation system described above, if the driver fails to hear the route guidance, or if the vehicle must turn right at the guidance intersection, but the recommended lane is the most left lane. As a result, the driver may be unable to drive the vehicle according to the lane guidance and end up driving in a lane other than the recommended lane by mistake. That is, it is sometimes, according to the conventional navigation system, it is impossible to drive the vehicle along the specified route.

Moreover, in the conventional navigation system described above, even if the vehicle is already traveling in the recommended lane, lane guidance is provided repeatedly. As a result, the driver may feel that the superfluous lane guidance is annoying.

Exemplary implementations of the broad principles described may allow a vehicle to travel reliably according to lane guidance and/or prevent the vehicle from being driven in a lane other than the recommended lane by mistake, without making the driver feel annoyed by superfluous lane guidance.

Exemplary implementations provide systems, methods, and programs that may search for a route to a destination and may set a recommended travel lane, based on the searched for route. The systems, methods, and programs may provide lane guidance to lead the vehicle into the recommended lane. The systems, methods, and programs may receive a current position of the vehicle and may determine a movement direction of the vehicle, based on the received current position and the recommended lane. Then, the systems, methods, and programs may determine whether to provide lane guidance based on the movement direction of the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary implementations will now be described with reference to the accompanying drawings, wherein:

<figref idrefs="DRAWINGS">FIG. 1</figref> is a diagram showing an exemplary navigation system according to an embodiment of the present invention;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a flowchart showing an exemplary lane guidance method; and

<figref idrefs="DRAWINGS">FIG. 3</figref> is an explanatory drawing of exemplary lane guidance.

DETAILED DESCRIPTION OF EXEMPLARY IMPLEMENTATIONS

<figref idrefs="DRAWINGS">FIG. 1</figref> shows an exemplary navigation system. As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the navigation system may include, for example, an automatic transmission control portion <b>10</b>. The automatic transmission control portion <b>10</b> may control a power train for changing gear at a predetermined transmission gear ratio such as, for example, a continuously variable transmission (CVT), an automatic transmission, and/or an electric drive system.

The navigation system may include, for example, an information terminal, such as, for example, an on-board navigation unit <b>14</b> mounted on a vehicle. The navigation system may include, for example, a network <b>63</b> and an information center <b>51</b> as an information provider.

The navigation unit <b>14</b> may include, for example, a GPS sensor <b>15</b> for detecting a current position of the vehicle, a memory (e.g., data storing portion <b>16</b>) for storing map data and various types of information, and a controller (e.g., navigation processing portion <b>17</b>) for performing various calculations such as navigation processing on the basis of input information. The navigation unit <b>14</b> may include, for example, a direction sensor <b>18</b> for detecting a vehicle direction, an operating portion <b>34</b> for receiving input from a user, a display portion <b>35</b> for displaying various images on a screen (not shown) to guide the driver, and an audio input portion (e.g., voice input portion <b>36</b>) for performing audio input. The navigation unit <b>14</b> may include, for example, an audio output portion (e.g., voice output portion <b>37</b>) for outputting various audio messages to aid the driver and a communication portion <b>38</b>. The GPS sensor <b>15</b>, the data recording portion <b>16</b>, the direction sensor <b>18</b>, the operating portion <b>34</b>, the display portion <b>35</b>, the voice input portion <b>36</b>, the voice output portion <b>37</b>, and the communication portion <b>38</b> may be connected to the navigation processing portion <b>17</b>.

The automatic transmission control portion <b>10</b>, a forward monitoring device <b>48</b> that is mounted at a predetermined position in the front part of the vehicle for monitoring the area in front of the vehicle, a rear view camera <b>49</b> that is mounted at a predetermined position in the rear part of the vehicle, an accelerator sensor <b>42</b> for detecting the degree of opening of an accelerator pedal (not shown), a brake sensor <b>43</b> for detecting the level of braking applied to the vehicle through a brake pedal (not shown), and a vehicle speed sensor <b>44</b> for detecting the vehicle speed may also be connected to the navigation processing portion <b>17</b>. Note that, for example, the accelerator sensor <b>42</b> and the brake sensor <b>43</b> may detect information related to vehicle operation by the driver.

The GPS sensor <b>15</b> may detect a current position on the earth by receiving a radio wave from a satellite and may also detect a time. However, a distance sensor, a steering sensor, and/or an altimeter (not shown) may be used independently or together instead of the GPS sensor <b>15</b>. A gyro sensor or a geomagnetic sensor may be used as the direction sensor <b>18</b>. Note that, these sensors are not needed when the GPS sensor has a function of detecting, for example, a vehicle direction and a vehicle speed.

The data storing portion <b>16</b> may include a map database including a map data file to store map data therein. The map data may include intersection data regarding intersections, node data regarding nodes, road data regarding road links, search data processed for searching, facility data regarding facilities, and feature data regarding features on a road. As used herein, the term “road link” refers to, for example, a road or portion of a road. For example, according to one type of road data, each road may consist of a plurality of componential units called links. Each link may be separated and defined by “nodes,” for example, an intersection, an intersection having more than three roads, a curve, and/or a point at which the road type changes.

Road features may include an object set or formed on a road that provides travel information to the driver or that provides travel guidance to the driver such as, for example, a line, a road sign, a crosswalk, a manhole, and/or a traffic light. The line may be a stop line indicating where a vehicle should stop, a line separating vehicular lanes, or a line indicating a parking space. The road sign may be an information sign indicating a direction of a lane by means of an arrow, a warning sign such as “STOP” to notify the driver of a stop line or a direction sign such as “the direction of XX” to provide directions to a location. The feature data may include position information indicating the positions of features by means of coordinates and/or image information indicating features by means of images. Note that, the stop line may include an entrance from a non-priority road to a priority road, a railroad crossing, and/or an intersection with a blinking red light.

The road data regarding the lanes may include lane data such as a lane number for each lane on roads and/or lane position information. The data storing portion <b>16</b> may store data for outputting predetermined information by the voice output portion <b>37</b>.

Further, the data storing portion <b>16</b> may include a statistical database including a statistical data file and/or a travel history database including a travel history data file, and statistical data is stored in the statistical data file as past record data as is travel history data in the travel history data file.

The statistical data may include a past record of traffic information, that is, history information indicating travel history. The statistical data may include various types of information, that is, for example, past traffic information provided by a road traffic information center (not shown) such as a VICS (Vehicle Information and Communication System), road traffic census information indicating traffic volume obtained by a road traffic census provided by the National Land and Transportation Ministry, and road timetable information provided by the National Land and Transportation Ministry, and such information may be used individually/collectively, modified, or undergo statistical processing, if needed. Note that, congestion prediction information for predicting traffic congestion may be added to the statistical data. In that case, detailed conditions such as date and time, day of the week, weather, various events, season, facility information (presence or absence of large facilities such as a department store and/or a supermarket) may be added to the history information to create the statistical data.

As data items for the statistical data, a link number for each of a plurality of road links, a direction flag indicating a travel direction, a type of information, a congestion degree at each of a plurality of predetermined times, a link required travel times indicating the lengths of time required to travel the road links at predetermined times, and/or average data of the link required time for each day of the week may be included.

The travel history data may be collected from a plurality of vehicles, that is, from the vehicle mounted with the navigation apparatus and/or other vehicles, by the information center <b>51</b>. The travel history data may include past record information indicating the travel record of roads along which each vehicle has traveled and is calculated and stored as probe data on the basis of travel data.

As data items for the travel history data, a link required travel time and a congestion degree for each road link at a predetermined time may be included. Note that, the travel history data may be added to the statistical data. Further, the congestion degree may be displayed as a congestion indicator, for example, “congested,” “crowded,” and “not congested,” indicating the degree of traffic congestion.

The data storing portion <b>16</b> may include a disk (not shown) such as a hard disk, a CD, a DVD, or an optical disk to store the various data described above and also include a head (not shown) such as a readout/writing head to read out/write various data. For example, a memory card may be used as the data storing portion <b>16</b>. Note that, an external storage device or a memory card may be one of the disks described above.

The map database, the statistical database, and the travel history database may be included in the data storing portion <b>16</b>. However, one or more of the map database, the statistical database, and the travel history database may be included in the information center <b>51</b> instead.

The navigation processing portion <b>17</b> may include, for example, a CPU <b>31</b> as a control device as well as a calculating device for controlling the whole navigation apparatus <b>14</b>, a RAM <b>32</b> as a working memory for helping the CPU <b>31</b> to perform various calculations, a ROM <b>33</b> for storing a control program and various programs for searching for a route to a destination or for route guidance, and a flash memory (not shown) for storing various data and programs. Note that, an internal storage device may be the RAM <b>32</b>, the ROM <b>33</b>, or the flash memory.

Various programs may be stored in the ROM <b>33</b> and various data may be stored in the data storing portion <b>16</b>. However, such programs and data may be stored on, for example, a disk. In this case, the programs and/or data may be read out from the disk and may be written to a flash memory. Therefore, the programs and/or data may be updated by changing the disk. Further, control program and/or data of the automatic transmission control portion <b>10</b> may be stored on the disk as well. Then the programs and data may be received through the communication portion <b>38</b> and stored in the flash memory of the navigation processing portion <b>17</b>.

By the driver's operation, the operating portion <b>34</b> may be used for correcting a current position when the vehicle starts moving, inputting a starting point and a destination, inputting a point to be passed, and activating the communication portion <b>38</b>. A keyboard or a mouse that is different from the display portion <b>35</b> may be used as the operating portion <b>34</b>. Also, a touch panel with image operating portions such as various keys, switches, and buttons may be used as the operating portion <b>34</b>. Such keys, switches, and buttons may be displayed on a screen of the display portion <b>35</b> and touched or clicked for a predetermined input operation.

A display may be used as the display portion <b>35</b>. In various screens displayed on the display portion <b>35</b>, for example, a current position of the vehicle as a vehicle position, a vehicle direction, a map, a searched route, guide information along the searched route, traffic information, a distance to a next intersection on the searched route, and/or a travel direction at the next intersection may be displayed. Further, operating instructions and guidance of operating menu/keys of the image operating portion, the operating portion <b>34</b>, and the audio input portion <b>36</b> as well as an FM multiplex telecasting program name may be displayed in the various screens of the display portion <b>35</b>.

The voice input portion <b>36</b> may include a microphone (not shown) to input necessary information by audio. The voice output portion <b>37</b> includes a speech synthesis device and a speaker (not shown) to output an audio message synthesized by the speech synthesis device for, for example, the searched route, guidance information, and/or traffic information.

The communication portion <b>38</b> may include a beacon receiver and/or an FM receiver. The beacon receiver (for example, electric wave beacon and/or optical beacon) may receive various types of information such as current traffic information and general information sent from, for example, the road traffic information center via, for example, an electric wave beacon device and/or optical beacon device provided along a road. The FM receiver may also receive such information as multiple broadcasts via an FM broadcast station. The traffic information may include, for example, congestion information, road sign information, parking lot information, traffic accident information, and/or information on the busy status of service areas. The general information may include, for example, news and weather reports. The beacon receiver and the FM receiver may be one unit provided as a VICS receiver, or each may be provided separately.

The traffic information may include a type of information, a mesh number to specify a mesh, a link number for specifying a road link which connects two points, for example, two intersections and for indicating the difference between inbound and outbound traffic on the road link, and link information indicating information corresponding to the link number. For example, when traffic information is congestion information, the link information may include data about the head of a traffic jam indicating a distance from the start point of the road link to the head of the traffic jam, the congestion degree, the length of the traffic jam indicating the distance from the head of the traffic jam to the end of the traffic jam, and a link required travel time indicating the length of time required to travel the road link.

The communication portion <b>38</b> may receive the map data, the statistical data, the travel history data, and various information such as traffic information and general information from the information center <b>51</b> through the network <b>63</b>.

The information center <b>51</b> may include, for example, a controller (e.g., server <b>53</b>), a communication portion <b>57</b> connected to the server <b>53</b>, and memory (e.g., database (DB) <b>58</b>). The server <b>53</b> may include a CPU <b>54</b>, an RAM <b>55</b>, and an ROM <b>56</b> as a control device and a calculating device. Data the same as the various data stored in the data storing portion <b>16</b> such as the map data, the statistical data, and the travel history data may be stored in the database <b>58</b>. The information center <b>51</b> may provide current traffic information and various information such as general information sent from the road traffic information center and travel history data collected from a plurality of vehicles (the vehicle mounted with the navigation apparatus and/or other vehicles) in real time.

The forward monitoring device <b>48</b> may include a laser radar, a radar such as a millimeter wave radar, and/or a supersonic sensor, and such radars and sensors may be used individually or collectively to monitor a vehicle in front of the vehicle mounted with the navigation apparatus, a stop line, and/or an obstacle. The forward monitoring device <b>48</b> may detect a relative vehicle speed to the vehicle in front of the vehicle mounted with the navigation apparatus, an approach speed to a stop sign/obstacle as area information and calculates the distance between both vehicles and the time required to reach the next vehicle.

The rear view camera <b>49</b> including a CCD sensor is attached to the rear part of the vehicle and the optic axis of the rear view camera <b>49</b> is directed downward to monitor the area behind the vehicle. The rear view camera <b>49</b> may image a vehicle traveling behind the vehicle mounted with the navigation apparatus, a building on the side of the road, and/or a structural object as well as a feature, create image data of such an object, and send the image data to the CPU <b>31</b>. The CPU <b>31</b> may read the image data, execute image processing, and determine each of the objects in the image as a specific object. A C-MOS sensor may be used instead of a CCD sensor.

Note that, the navigation system, the navigation processing portion <b>17</b>, the CPUs <b>31</b> and <b>54</b>, and the server <b>53</b> may function as a controller individually or collectively to execute processing using various programs and data. The data storing portion <b>16</b>, the RAMs <b>32</b> and <b>55</b>, the ROMs <b>33</b> and <b>56</b>, the database <b>58</b>, and/or the flash memory may function as a memory. For example, an MPU may be used as a processing device instead of the CPUs <b>31</b> and <b>54</b>.

Next, a basic operation of the navigation system with the structure determined as described above will be described.

When the navigation apparatus <b>14</b> is activated by the driver' operation of the operating portion <b>34</b>, the CPU <b>31</b> may read a current vehicle position detected by the GPS sensor <b>15</b> and a vehicle position detected by the direction sensor <b>18</b>, and may initialize various data. Next, the CPU <b>31</b> may determine on which road link the current position is located on the basis of a movement locus of the current position, and a shape and a position of each road link of roads around the current position, and may specify the current position. The current position may be specified, for example, on the basis of positions of each feature that is imaged by the rear camera <b>49</b>.

The CPU <b>31</b> may read image data from the rear camera <b>49</b> and may recognize a feature in an image within the image data. The CPU <b>31</b> may calculate the distance between the rear camera <b>49</b> and the actual feature on the basis of the position of the feature in the image. The CPU <b>31</b> may then read the distance described above, further read feature data from the data storing portion <b>16</b>, obtain the coordinates of the feature, and specify the current position on the basis of the coordinates and the distance.

The CPU <b>31</b> may detect a current traveling lane on the basis of the recognized feature in the image data and the feature data read out from the data storing portion <b>16</b>.

Note that, the CPU <b>31</b> may read an output from the geomagnetic sensor, determine whether there is an object which is made of a ferromagnetic material such as a predetermined manhole on the road on the basis of the output from the sensor, and detect a traveling lane on the basis of the determination. Further, the current position may be detected with high accuracy by using the high-precision GPS sensor <b>15</b>. As a result, the traveling lane may be detected on the basis of the result of the detection of the current position. If needed, while image processing is executed for image data of display lines, the traveling lane may be detected by using the output from the geomagnetic sensor and the current position collectively.

The CPU <b>31</b> may read out and obtain the map data from the data storing portion <b>16</b> or to receive and obtain the map data from the information center <b>51</b> through the communication portion <b>38</b>. Note that, when obtaining the map data from the information center <b>51</b>, the CPU <b>31</b> may download the received map data on a flash memory.

The CPU <b>31</b> may display various screens on the display portion <b>35</b>. For example, the CPU <b>31</b> may display a map screen on the display portion <b>35</b> and display an area map as well as the current vehicle position and the vehicle direction on the map screen. As a result, the driver may drive the vehicle on the basis of the map, the vehicle position, and the vehicle direction.

When the driver inputs a destination by operating the operating portion <b>34</b>, the CPU <b>31</b> may set the destination. If needed, a starting point may be input and set. Further, if a predetermined point is stored in advance, the stored point may be set as a destination. When the driver inputs a search condition by operating the operating portion <b>34</b>, the CPU <b>31</b> may set a search condition.

After setting the destination and the search condition, the CPU <b>31</b> may read out the current position, the destination, and the search condition, read search data from the data storing portion <b>16</b>, search for a route from the starting point (e.g., the current position) to the destination on the basis of the search condition, the read current position, the destination, and the search data. The CPU <b>31</b> may then output route data indicating the searched route. In this case, a route that has the minimum total amount of link costs for road links on the route may be chosen as the search route.

When a road has a plurality of lanes and a current traveling lane is detected among the lanes, the CPU <b>31</b> may search for a route including the traveling lane. In this case, the lane number of the traveling lane may be included in the route data.

Note that, the information center <b>51</b> may execute route searching processing. The CPU <b>31</b> may send the current position, the destination, and the search condition to the information center <b>51</b>. After the information center <b>51</b> receives the current position, the destination, and the search condition, the CPU <b>54</b> may read out search data from the database <b>58</b>, searches for a route from the starting point to the destination on the search condition on the basis of the current position, the destination, an the search data, and outputs route data indicating the searched route. Then the CPU <b>54</b> may send the route data to the navigation apparatus <b>14</b>.

The CPU <b>31</b> may provide guidance along the route. The CPU <b>31</b> may read the route data and may display the searched route on the map screen on the basis of the route data.

When the vehicle needs to turn right or left at a predetermined intersection while the route guidance is performed, the intersection is set as a guidance target point and as a turn intersection. The CPU <b>31</b> may determine whether there is an intersection at which the vehicle needs to turn right or left on the basis of the searched route of the route data. When there is such intersection, the intersection may be set as the turn intersection by the CPU <b>31</b>. Note that, as the turn intersection, any intersection at which an entering road and a plurality of exiting roads are crossed with each other such as a junction of three roads, a right angle cross road, and a junction of five roads may be included.

When the route is searched at the lane level, the CPU <b>31</b> may recommend a lane. For example, a recommended traveling lane for passing through the turn intersection such as a suitable lane for entering to the turn intersection or a suitable lane for leaving from the turn intersection may be selected and set as a recommended lane. The CPU <b>31</b> may display the searched route on the map screen, display an enlarged view of the traveling road of the vehicle in a predetermined range of the map screen, and perform the lane guidance using the road enlarged view. In the road enlarged view, each lane and the set recommended lane may be displayed.

The CPU <b>31</b> may output audio route guidance from the voice outputting portion <b>37</b>. The CPU <b>31</b> may set one or more than one route guidance points at each point which is in front of the turn intersection on the searched route and is a predetermined distance away from each other. When the vehicle arrives at each of the route guidance points, the route guidance for the turn intersection whose content is preset corresponding to each of the route guidance points may be performed. For example, route guidance for a distance from the vehicle position to the turn intersection or for a right or left turn at the turn intersection may be performed. When a recommended lane is set, The CPU <b>31</b> may perform the lane guidance whose content is preset corresponding to each of the route guidance points. For example, the lane guidance for each of recommended lanes between the vehicle position and the turn intersection or the lane guidance for a recommended lane coming after the turn intersection may be performed.

The CPU <b>31</b> may read out intersection data, display an enlarged view of the turn intersection within a predetermined area of the map screen before the vehicle arrives at the turn intersection, and perform route guidance using the intersection enlarged view. In this case, an area map around the turn intersection, the searched route, and a landmark such as a facility for recognizing the turn intersection may be displayed on the intersection enlarged view. When the entering road and/or the exiting roads at the turn intersection have a plurality of lanes and the lane guidance is being performed, The CPU <b>31</b> may display a recommended lane on the intersection enlarged view. Therefore, the intersection data may include data of the name of the intersection, the entering road, the exiting roads, a presence or absence of a traffic light, and the type of the traffic light.

As discussed above, when lane guidance is provided by voice, if the driver fails to hear the route guidance, or if the vehicle must turn right at the guidance intersection, but the recommended lane is the most left lane, the driver may be unable to drive the vehicle according to the lane guidance and end up driving in a lane other than the recommended lane by mistake. As result, the driver will be unable to drive the vehicle along the specified route.

Also, as discussed above, when the driver has changed into the recommended lane, if lane guidance is provided repeatedly, even if the vehicle is already traveling in the recommended lane, the driver feels that the superfluous lane guidance is annoying.

Therefore, according to this exemplary implementation, lane guidance may be provided in accordance with the movement of the vehicle.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a flowchart showing an exemplary lane guidance method. <figref idrefs="DRAWINGS">FIG. 3</figref> is an explanatory drawing of lane guidance. The exemplary method may be implemented, for example, by one or more components of the above-described system. However, even though the exemplary structure of the above-described system may be referenced in the description, it should be appreciated that the structure is exemplary and the exemplary method need not be limited by any of the above-described exemplary structure.

In <figref idrefs="DRAWINGS">FIG. 3</figref>, the reference numerals pr<b>1</b> to pr<b>3</b> denote vehicle positions, the reference numeral r<b>1</b> denotes the road, the reference numeral Rt denotes the specified route, the reference numerals k<b>1</b> to k<b>4</b> denote lanes of the road r<b>1</b>. As shown in <figref idrefs="DRAWINGS">FIG. 3</figref>, the lane k<b>4</b> is the recommended lane.

When, for example, the recommended lane k<b>4</b> is set by the CPU <b>31</b> and lane guidance is executed to lead the vehicle into the recommended lane, the CPU <b>31</b> determines the movement of the vehicle. For that purpose, the CPU <b>31</b> may read the host vehicle position pr<b>1</b> at the time that lane guidance is executed, and may starts measuring time by means of a timer. When a prescribed time interval t<b>1</b> has elapsed after the lane guidance was executed, the CPU <b>31</b> may read the host vehicle position (e.g., pr<b>2</b> or pr<b>3</b>). Note that the time interval t<b>1</b> may be set only to a length of time at which the direction of movement from the host vehicle position pr<b>1</b> can be determined, for example, the time required for the vehicle to move into an adjacent lane.

Next, the CPU <b>31</b>, based on the relationship between the recommended lane and the host vehicle position pr<b>2</b> or pr<b>3</b>, may determine the direction of vehicle movement, for example, by determining whether the number of lane changes necessary to move into the recommended lane from the host vehicle position in the lane k<b>3</b> or the lane k<b>1</b> has changed.

As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the direction of vehicle movement may be determined by determining whether the number of lane changes necessary to be in the recommended lane k<b>4</b> has decreased (step S<b>1</b>). Specifically, if the number of lane changes has decreased (step S<b>1</b>=Yes), the CPU <b>31</b> may conclude that the vehicle has moved in a direction of approaching the recommended lane (hereinafter called the approaching direction), as shown by arrow A in <figref idrefs="DRAWINGS">FIG. 3</figref>. If the number of lane changes has not changed (step S<b>1</b>=No), the CPU <b>31</b> may conclude that the vehicle has moved in a direction parallel to the recommended lane (hereinafter called the parallel direction). If the number of lane changes has increased (step S<b>1</b>=No), the CPU <b>31</b> may conclude that the vehicle has moved in a direction of away from the recommended lane (hereinafter called the diverging direction), as shown by arrow B in <figref idrefs="DRAWINGS">FIG. 3</figref>.

If the vehicle has moved in the approaching direction (Step S<b>1</b>=Yes), the vehicle may be considered to be on course, and the CPU <b>31</b> may suspend lane guidance for a prescribed interval. For this purpose, the CPU <b>31</b> may use the point in time when the movement direction was determined as a guidance suspension starting time and may starts measuring time using the timer. For this purpose, the CPU <b>31</b> may also take the vehicle position at the point in time when the movement direction was determined and records it in the RAM <b>32</b> as a guidance suspension starting position. Then, the CPU <b>31</b> may not execute lane guidance, for example, until the vehicle has traveled for a fixed time interval t<b>2</b> after the guidance suspension starting time and/or for a fixed distance Lx from the guidance suspension starting position.

It should be appreciated that even if the time interval t<b>2</b> elapses, if the vehicle has not traveled the distance Lx, it may be assumed that traffic is congested. As a result, the CPU <b>31</b> may not execute lane guidance until the vehicle has also traveled the distance Lx. Similarly, for example, even if the vehicle has traveled the distance Lx, if the time interval t<b>2</b> has not elapsed, it may be assumed that the driver remembers the most recent lane guidance, the CPU <b>31</b> may not execute lane guidance until the time interval t<b>2</b> has also passed. While both the time interval t<b>2</b> and the distance Lx may be used, alternatively, only the time interval t<b>2</b> or the distance Lx may be used.

By contrast, when the vehicle has moved in the parallel direction or the separating direction (Step S<b>1</b>=No), the vehicle may be considered to be headed off course, and the CPU <b>31</b> may execute lane guidance.

According to the above-described exemplary method, when the vehicle has moved in the approaching direction in relation to the recommended lane, lane guidance may be suspended. As a result, lane guidance is not executed repeatedly in cases where, for example, the vehicle is simply in the process of moving into the recommended lane and/or the vehicle is already traveling in the recommended lane. Because there is not repeated voice guidance, the driver will not be annoyed by superfluous lane guidance.

Moreover, according to the above-described exemplary method, because lane guidance is executed when the vehicle has moved in the parallel direction or the separating direction (e.g., the driver has failed to hear previous lane guidance, or the vehicle must turn right at the guidance intersection, but the recommended lane is the most left lane), the vehicle can reliably be driven according to the lane guidance. It is therefore possible to prevent the vehicle from being driven in a lane other than the recommended lane by mistake, so the vehicle can be driven along the specified route.

While various features have been described in conjunction with the examples outlined above, various alternatives, modifications, variations, and/or improvements of those features and/or examples may be possible. Accordingly, the examples, as set forth above, are intended to be illustrative. Various changes may be made without departing from the broad spirit and scope of the underlying principles.